This invention relates to electronic musical instruments, and in particular to those of the keyboard type as exemplified by an electronic organ. The invention deals more specifically with such an instrument capable of automatically generating or synthesizing notes that bear the same names as those of keys played on one keyboard or key group but which are in closer octaval correlation (octave region) with the notes of keys played simultaneously on another keyboard or key group.
The above automatically generated notes are referred to as "fill notes", and tones corresponding thereto are termed "fill tones", since they supplement, in a sense, the notes played on the second mentioned keyboard or key group.
For a better understanding of such fill notes or fill tones, there may be considered a usual electronic musical instrument having upper and lower keyboards or manuals by way of example. As the performer plays melodies on the upper keyboard and accompaniment chords on the lower keyboard, the fill tones sounded automatically will be of the same note names as the chordally related tones played on the lower keyboard but will be more intimately associated octavely (in the near octave region) with the melody tones played on the upper keyboard.
D. R. Moore U.S. Pat. No. 3,929,051, entitled "Multiplex Harmony Generator" and dated Dec. 30, 1975, describes and claims such an instrument capable of fill-note generation. For the production of chord tones octavely correlated with melodies, the instrument according to this U.S. patent relies on data identifying the chordally related notes to be sounded as fill tones in terms of timewise location of the pulses. A brief discussion of the D. R. Moore U.S. patent follows in order to better distinguish the present invention therefrom.
In the prior patented instrument the key switches of the upper keyboard are scanned one after another in the order of the key arrangement (alignment) on the keyboard. During each scanning cycle of the upper key switches, the key switches of the lower keyboard are repeatedly scanned only as to the 12 note names (C through B) in all octaves commonly (simultaneously). Upon depression of any key a pulse is generated at the corresponding one of successive positions in time referred to as the time slots. The time slot corresponding to the highest or representative one of the upper keys played together (depressed concurrently) is followed by a time interval equivalent to one octave, into which there are inserted the pulses indicative of the note names of the depressed lower keys. Thus the chord notes played on the lower keyboard are transformed into fill notes falling within an octave below the highest melody note played on the upper keyboard.